Knowing when to dose can be a challenge for many farmers. The weather this year has been unfavourable, but the late turnout and cold summer has meant that many farmers are learning to adapt to their dosing regimes.
Parasitic gastroenteritis is commonly caused by gutworms Ostertagia and Cooperia.
Their lifecycle depends on the presence of host animals and favourable climate conditions. As pasture contamination builds up, the risk of disease increases throughout the summer.
As a result, the two peak periods of risk are three to four weeks post turnout and then again in July.
“This year, the combination of late turnout and a cool start to the summer has meant that the worm challenge hasn’t followed usual patterns,” explained Norbrook technical adviser, Maura Langan.
“Some farmers have been able to hold off on the first dose and performed FEC tests before deciding to treat.”
Calves in their first grazing season are completely naive and therefore are at high risk of parasitic infection.
It is recommended that young cattle are sufficiently exposed to infection before being wormed to allow natural immunity to develop.
Older, second season cattle should have acquired some level of immunity to gutworms, so the need to treat should be balanced between the effects on the wellbeing and performance of cattle and a responsible approach to the prescribing and use of anthelmintics.
“Although we maybe haven’t seen peak infection just yet, cattle have been grazing and picking up low levels of worms.
“If we do see temperatures pick up in the next couple of weeks, it’s possible that we’ll see a sudden increase in numbers resulting in the need to dose quickly,” warned Maura.
Knowing when to dose
Short-acting wormers such as levamisole (Levacide Low-Volume) can be useful when balancing exposure and treatment.
Levamisole has no persistency, so may be a suitable initial grazing treatment, or ‘primer dose’ that allows immunity to develop following exposure to gutworms earlier in the season.
Persistent wormers continue to protect cattle from re-infection after treatment. Actives like doramectin that have persistency (Taurador Pour-On) mean further worming may not be necessary for another six to eight weeks following treatment.
“A persistent wormer like Taurador can offer effective, practical treatments for management groups not being handled regularly and provide effective worm control throughout a potential risk period.
“As always, mid-summer also brings a high risk of lungworm, so remain vigilant for the sound of coughing in all stock, but most especially calves,” Maura added.
The rate of development of lungworm larvae passed out in the faeces is affected by weather conditions. If warm (20°C) and humid conditions prevail, infection can be rapid.
Calves are completely naive and can acquire a dangerous level of infection within 24 hours of grazing contaminated pasture.
Larvae may be dispersed from the dung pat by a fungus or by the splashing effects of rain. This means that pastures can become contaminated with infective larvae very quickly and peaks in lungworm infection often occur when heavy rain follows a dry spell.
Lungworm causes coughing and laboured breathing and if left untreated can result in death or long-term debility. Lungworm in growing cattle can incur losses of between €60 and €120/head.
“Lungworm infection, in comparison to gutworm, is unpredictable. It affects both young and adult animals, can cause long-term effects and even death.
The persistency of immunity to lungworm can be variable, with susceptibility to reinfection leading to severe respiratory signs when cattle are exposed to a heavy larval challenge from pasture.
It is this reinfection syndrome that is responsible for coughing in adult dairy cows commonly referred to as ‘coughing cows’.
Farmers need to remain vigilant to the clinical signs of lungworm and treat the whole group promptly,” explained Maura Langan.
All classes of wormer are indicated for treatment of lungworm. Your vet may recommend treatment with a levamisole (Levacide Low Volume) due to the active’s unique mode of action.
It kills the lungworm by spastic paralysis which allows for the dead lungworm to coughed up more easily.
As always, speak to your vet to seek advice that is specific to your farm.
